The invention relates to a REMA objective. This is an objective with which a Reticle Masking (REMA) device is imaged in the plane of the reticle which carries the structured mask for lithography. The region which is lighted on the reticle is thus sharply delimited. The reticle masking device is usually constructed with adjustable blades. The imaging usually gives enlargement.
A REMA objective is used in microlithography projection illumination devices (steppers or scanners).
An illuminating device for a microlithography projection illumination device is known from DE-U-94 09 744 in it there are provided, in the following sequence: light source, shutter, coupling lens (zoom-axicon), glass rod as integrator, reticle masking system, REMA objective for imaging on the reticle the intermediate field plane located in the reticle masking system, containing a first lens group, a pupil intermediate plane, a second lens group, a deflecting prism, a third lens group, and the reticle plane with the reticle. After this there follows a projection objective, which normally reduces and which containsxe2x80x94for example with a non-telecentric inputxe2x80x94an internal pupil plane, and then the wafer in the image plane.
In the system according to EP 0 526 242 A1, a projection objective is first provided after the integrator, here a honeycomb condenser, before the reticle masking system follows. The reticle masking system is optically conjugate to the reticle plane via two lens groups and a mirror, and is thus imaged. Likewise, the diaphragm at the exit of the integratorxe2x80x94the secondary light sourcexe2x80x94is imaged by the two lens groups and portions of the projection objective on the pupil of the projection objective. Nothing is said there about imaging errors.
A high aperture catadioptric reduction objective for microlithography is described in the Applicant""s WO 95/32446; its embodiment example according to FIG. 3 and Table 2 is exactly matched by the embodiment example of a REMA objective shown here.
The Laid-Open Patent Application DE-A 195 48 805 of Dec. 27, 1995, which was first published after the priority date, describes REMA objectives with exclusively spherical lens surfaces. The embodiment example there has 13 lenses and is very similar in its optical properties to the embodiment example shown here (FIG. 1). Both REMA objectives predominantly match, as regards their pupil function, the projection objective of WO 95/32446.
U.S. Pat. No. 5,742,436 corresponding to the said WO document; U.S. Pat. No. 5,982,558 corresponding to DE-A 195 48 805; and U.S. Pat. No. 5,646,715 corresponding to DE-U 94 09 744, are therefore expressly a part of the disclosure of this patent application.
The invention has as its object to provide a REMA objective which has considerably fewer boundary surfaces, at which reflection losses occur, and a considerably smaller glass path, in which absorption takes place, and thus a substantially improved degree of transmission efficiency. This is not to lead to any curtailment of the optical properties.
A REMA objective according to this invention has a few, at most four or five, aspheric elements.
A REAM objective according to the invention has an enlargement of three times through eight times, a light-conduction value greater than 10 mm, in which imaging of a bright/dark edge from an object plane onto a reticle plane results in an edge course whose brightness values of 5% and 95% are mutually separated by less than 2% of the image field diameter, including no more than 10 lenses, including 1 to 5, aspheric surfaces.
It is known per se that aspheric elements open up new correction possibilities, and lenses can be saved thereby. However, it is also clear that aspheric elements drastically increase the cost of production and of quality testing, so that they have to be used sparingly, with due regard to their number and their deviation from a spherical shape.
A respective reduction of the number of lenses and the glass path to below 60%, with only three to four, at most five, aspheric elements, whose deviations from sphericity are moderate, has surprisingly been achieved. Furthermore, the high requirements on a REMA objective are then fulfilled, and the efficiency (the transmission) is nevertheless clearly increased.
Claim 1 makes this circumstance clear. Claim 2 is oriented to the structure, with condenser, intermediate, and field lens portions.
Dependent claims 3-15 relate to advantageous embodiment examples.
Claim 2 quantifies the reduced glass path to under 30%, preferably under 25%, of the object-reticle distance.
The REMA objective according to the invention reproduces a predetermined pupil function with values of sin(I) in the range of xc2x110 mrad with deviations of less than xc2x11 mrad, including deviations of less than xc2x10.3 mrad. Claims 7 and 8 then relate to conforming to the specially preferred environment with REMA at the exit of a glass rod or with a reducing catadioptric projection objective.
Claim 15 relates to the conformity to the pupil function of a projection objective with very good telecentricity with very small deviations. The small deviations from parallelism of the main beams of the projection objective are thus very well met by the REMA objective.
Independent claim 16 takes up this good conformity to the associated projection objective of the REMA objective with the described few elements, for a whole microlithography projection illumination device.